Vertical Deformation of the 2019 M6.4 Searles Valley and M7.1 Ridgecrest Earthquakes

Bridget R. Smith-Konter, Lauren A. Ward, Xiaohua Xu, & David T. Sandwell

Published August 15, 2019, SCEC Contribution #9869, 2019 SCEC Annual Meeting Poster #237

On July 4-5, 2019, the M6.4 and M7.1 Searles Valley and Ridgecrest earthquake sequence ruptured a geometrically complex 50 km long system of faults within the Eastern California Shear Zone (ECSZ). These conjugate events resulted in several meters of strike-slip and dip-slip along a fairly complex rupture, extending from the surface down to 15 km. Coseismic geodetic observations reveal 500+ mm of horizontal surface slip and at least 35 mm of vertical uplift at near-field station P595, located 10 km from the rupture zone. Some 70+ km away, smaller but still measurable subsidence and uplift motions (~8-12 mm) were also recorded, as predicted by far-field elastic dislocation theory. Similarly, over the next several months to years, vertical velocity transients are anticipated, characteristic of postseismic viscoelastic relaxation of the lower crust and upper mantle. To study this behavior and further probe the rheological properties of the ECSZ, we first performed a co-seismic slip source inversion of both events using GNSS and InSAR (Sentinel-1/ALOS-2) line-of-sight deformation data. The modeled vertical coseismic deformation field of the Ridgecrest earthquake sequence reveals alternating quadrants of deformation (+/- 35 mm) that straddle the rupture and span a wide (~200 km) region of the ECSZ. To study the postseismic response, we utilize a 4-D semi-analytic viscoelastic deformation model that simulates lateral variations in elastic plate thickness. As a starting model, we assume a 40 km thick elastic plate for the Western Basin and Range and Mojave bocks and allow contributions of a thicker elastic plate from the nearby Sierra Nevada block, consistent with heat flow data and seismically imaged LAB depths. Based on vertical velocity observations from previous regional M7 events (i.e., Landers, Hector Mine, El Major-Cucapah), vertical deformation responding to mantle viscosities as low as 10^17 Pa-s are expected for the first 6-12 months. However, vertical time series data over the next several months to years will be required to confirm this anticipated behavior. Moreover, forward modeling of this event suggests that measureable vertical postseismic transients could be observed several 10s of kms from the Ridgecrest rupture for the next several years.

Citation
Smith-Konter, B. R., Ward, L. A., Xu, X., & Sandwell, D. T. (2019, 08). Vertical Deformation of the 2019 M6.4 Searles Valley and M7.1 Ridgecrest Earthquakes. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Ridgecrest Earthquakes